1. Field of the Invention
The present invention is directed to an image forming apparatus and a heater control method.
2. Description of the Related Art
Various on/off control techniques for a heater for a fixing device or the like of an image forming apparatus, such as a copying machine, a printer, and a multifunction peripheral (MFP), have been known. The human eye is most sensitive to light fluctuations in the frequency range near 10 Hz having its center at 8.8 Hz. With recent image forming apparatuses, heater-on/off control timing is set so as to avoid the frequency range where the human eye is sensitive to flicker or such that frequency band is shifted to reduce flicker to a minimum.
For instance, a technique of half-wave control for reducing flicker due to heater control and maintaining low-flicker level stably has been known (for example, Japanese Patent No. 3316170). Under the half-wave control, for example, ten half wavelengths near 10 Hz where the human eye is sensitive to flicker are set as a heater on/off control cycle, and a high-frequency heater on/off pattern designed to avoid a frequency band around 10 Hz is used as a heater on/off pattern within the control cycle.
However, such conventional heater on/off control as discussed above is disadvantageous in that if, in the half-wave control, all half-waves are allocated to heater-on during an initial period after start of the heater on/off control, inrush current undesirably flows when a heater-off state is changed to a heater-on state. In spite that it is desirable to decrease disturbance voltage, the inrush current increases the disturbance voltage, making it difficult to maintain low-flicker level stably.